The present invention relates generally to centrifuges, and more specifically, but not exclusively concerns a centrifuge with a split shaft construction that simplifies centrifuge maintenance and at the same time permits the use of smaller bushings, which results in higher speeds that enhance the efficiency of the centrifuge in the removal of particulate matter from fluids.
Centrifuges are used in a variety of environments and applications in order to separate particulate matter from fluids. For instance, centrifuges are used to separate out particulate matter from lubricants in engines in order to prolong the life of the engine. When designing a centrifuge, rotational or operational speed of the centrifuge is always a concern. Generally, higher rotational speeds in the centrifuge tend to improve the separation efficiency of particulate matter from fluids, and conversely, lower speeds tend to reduce separation efficiency. A number of design considerations or factors may affect the operational speed of a centrifuge. Among these factors, one is the size of the bushings used in the centrifuge. In one typical centrifuge design, the centrifuge includes a fixed central shaft about which the rest of the components of the centrifuge, such as its rotor shell, rotate. A pair of bushings are usually fitted on opposite ends of the rotor in order to minimize friction between the shaft and the rotor shell. Bushing races are also formed at the opposite ends of the rotor, and the bushings engage the shaft at the races to minimize friction between the bushings and the shaft. Smaller bushing sizes in general permit higher operational speeds in the centrifuge, thereby improving separation efficiency; while larger bushing sizes usually reduce the operational speed of the centrifuge, which in turn reduces separation efficiency. The size or diameter of the shaft on which the bushings are fitted is a major factor that controls bushing size, and the strength of the shaft is always a concern that is weighed against shaft size when designing a centrifuge.
Traditional centrifuge shaft designs have been limited to two primary configurations, a shaft-spud assembly design (FIG. 1) and a one-piece shaft design (FIG. 2). In a shaft-spud assembly 30 design of FIG. 1, a shaft 31 is threadedly engaged to a spud 32. At one end, the shaft 31 has a housing collar 35 that is used for securing the shaft 31 to the housing of the centrifuge. Near the collar 35, the shaft 31 has a race surface 37 against which one of the bushings engages. In FIG. 1, the shaft 31 defines a fluid passageway 38 with outlet holes 39 for supplying fluid to the centrifuge. Opposite the collar 35 and around the fluid passageway 38, the shaft 31 has external threading 40 so that the shaft 31 can be secured inside a threaded opening 41 in the spud 32. The spud 32 has a race surface 42 around which the other bushing of the centrifuge is received and a retention collar 43 for retaining the bushing. As shown, the spud 32 has a threaded end 45 that is used to secure the centrifuge to other engine components, such as an engine block. Usually, the spud 32 is secured to the bottom of the centrifuge. Referring to FIG. 1, the spud 32 further defines a fluid inlet passageway 47 that supplies fluid to fluid passageway 38 in the shaft 31.
There are a number of drawbacks associated with the shaft-spud 30 design. For example, since the spud 32 is attached to the shaft 31 where the walls of the shaft 31 are relatively thin due to the fluid passageway 38, the spud 32 has to be relatively large. As a consequence, the larger sized spud 32 has a larger diameter race 42, which in turn increases the size of the bushing. As mentioned above, the larger sized bushing reduces the operational speed of the centrifuge, thereby reducing particulate separation efficiency of the centrifuge.
In the unitary or one-piece shaft 50 design of FIG. 2, smaller bushings (as compared to the shaft-spud assembly 30) can be used because the components of the spud 32, such as the collar 43 and race 42, are integrally formed on the shaft 50. However, many negative attributes arise with the one-piece shaft 50 design. For example, assembly and disassembly of the centrifuge becomes more difficult, especially in tight conditions, such as cramped engine compartments. Routine maintenance of centrifuges typically involves disassembly of the centrifuge housing assembly so that the used centrifuge rotor can be removed and replaced with a new, clean rotor. As illustrated in FIG. 2, the one-piece shaft 50 has a threaded end 51 on which a component similar to the collar 35 in FIG. 1 is secured, which in turn secures the shaft to the housing of the centrifuge. In one manner of disassembling the centrifuge, the collar component is removed from threaded end 51 of the shaft 50 so that the centrifuge rotor can be slid off the shaft 50. Due to the one-piece structure of the shaft 50, these components have to clear the entire length of the shaft 50 before they can be removed. As should be appreciated, the one-piece shaft 50 design makes removal of the centrifuge rotor extremely difficult, if not impossible, in cramped conditions. Thus, there remains a need for improvement in this field.